1. Field of the Invention
This invention relates to asphalt and concrete cutting heads or milling mandrels supported by and in use with various heavy machinery, and particularly to an asphalt and concrete milling mandrel specifically designed for cutting and pulverizing reinforced concrete.
2. Background of the Invention and Related Art
Asphalt milling is a technique currently employed to remove asphalt pavement for reconstruction or resurfacing, and for accessing buried utility lines. The technique involves the removal of asphalt pavement through the use of a cold planer, which can remove approximately ½ inch to 12 inches of pavement surface during a particular pass. A cold planer typically includes a barrel-like attachment, referred to as a milling mandrel or milling head, having a plurality of bits that are affixed to the exterior surface of the mandrel. The bits are exposed to the asphalt when the mandrel is in operation. Each bit has a hardened or carbide tipped end, a stem, and a flat end at the bottom of the stem. Bits are attached to mandrels by their insertion into channels or blocks, which are attached to the mandrels. The stem of the bit has a spring collet surrounding it. When the bit is forced into a channel in the bit block and pressed down through the shaft, the spring collet squeezes against the stem to tightly fit the stem within the channel. Between the stem and the bit's tipped end, there is an annular space on the bit that engages a lipped sector of the top end of the shaft and locks the bit into the shaft. This prevents the bit from leaving the shaft. Unfortunately, due to wear and tear, bits do not last long. Though they can last as long as several hours, oftentimes they need replacement after only fifteen minutes of mandrel operation. For instance, when an operator of a pavement grinder hits a manhole, many bits need replacement.
The cold planer could be coupled to a host vehicle (e.g., heavy machinery, such as a backhoe, a loader, or a skid-steer) or be self-propelled The mandrel rotates and is pushed into the pavement by the vehicle, causing the bits to engage and grind up the asphalt. Once ground, the asphalt can then be easily removed and replaced. The vehicle pushes the cold planer as the mandrel rotates to grind a trench in the asphalt pavement.
While the above milling device with its associated milling head are well suited to cut materials comprised of concrete and asphalt only, there are many instances when asphalt and concrete is reinforced using one or more reinforcement members, such as grid iron, rebar, etc. In these situations, the cutting or milling head is less equipped to efficiently cut or mill the reinforced material. Indeed, the situation where the asphalt milling or cutting device is required to mill and/or cut reinforced concrete or asphalt serves to exacerbate the problem discussed above.
Although bits on many milling heads are comprised of a hardened or carbide tip or end, any contact with various reinforcement members (typically comprised of steel or other metals) existing within the asphalt or concrete during operation of the milling device will damage and often destroy the bits as conventionally arranged and constructed. This is because the cutting or milling head is not intended to be used to cut through or to accommodate reinforcement members. As such, in the event of milling or cutting reinforced concrete or asphalt the bits existing on the mandrel must be changed much more frequently, thus making the project much more difficult to finish, as well as significantly increasing the costs of operation and the project.